MD_DataIdentification

Phase two will consist of post processing of the data collected. Aeroquest Optimal,
Inc. shall process the digital elevation data from a precision airborne (LIDAR) survey
within the entire project area. The proposed project area is approximately 6.3 million
acres. The purpose of the survey is to obtain measurements of the bare ground surface,
as well as top surface feature elevation data for providing geometry input to USACE
hydraulic modeling program. This project for USACE, Vicksburg District was to provide
digital orthophotography using DMC imagery for approximately 4,120 square miles located
in NW Mississippi at a 2-foot pixel resolution.

These data depict the elevations at the time of the survey and are only accurate for
that time. Users should be aware that temporal changes may have occurred
since this data set was collected and some parts of this data may no longer represent
actual surface conditions. Users should not use this data for critical
applications without a full awareness of its limitations. Any conclusions drawn
from analysis of this information are not the responsibility of NOAA or any of its
partners. These data are NOT to be used for navigational purposes.

For redundancy and accuracy purposes, the airborne GPS data were processed from two
base stations using POSGPS from Applanix, Inc. The agreement between a minimum of
two solutions checked or combined between a minimum of two stations was better than
10 cm in each of X, Y, and Z. These trajectories were used in the processing of the
inertial data. The inertial data were processed using POSProc from Applanix, Inc.
This software produces an SBET (?smooth best estimate of trajectory?) using the GPS
trajectory from POSGPS and the roll, pitch and heading information recorded by the
POS (Position Orientation System). DASHMap uses the SBET to generate a set of data
points for each laser return in the LAS file format. Each data point is assigned an
echo value so it can be segregated based on the first and last pulse information.
This project?s data were processed in strip form, meaning each flight line was processed
independently. Processing the lines individually provides the data analyst with the
ability to QC the overlap between lines. Each strip was then imported into a project
using TerraScan (Terrasolid, Ltd.) and the project management tool GeoCue (GeoCue
Corp.). By creating a project the various flightlines are combined while breaking
the dataset as a whole into manageable pieces. This process also converts the dataset
from the geographic coordinate system (NAD83) to the State Plane Coordinate System
(NAD83), Mississippi West, Feet, and utilizing standard ESRI transformations. The
ellipsoid height values were converted to NAVD88, Feet, orthometric values using Geoid03,
provided by NGS. Individual lines were then checked against adjacent lines and intersecting
control lines to ensure a cohesive dataset. The data from each line were then combined
and LiDAR intensity images were produced to visually check the horizontal positioning
of the LiDAR data. Stereo pairs were generated from the LiDAR intensity data using
Geocue and LiDAR1CuePac (Geocue Corp.). LiDARgrammetry was then utilized to collect
breaklines where necessary along hydro features to support the contour generation.
These breaklines were collected as a 3D element in the MicroStation (Bentley Systems,
Inc.) environment utilizing ISSD (Z/I Imaging). A Triangular Irregular Network (TIN)
was generated using the final surface data. Contours were then created from the TIN
utilizing TerraModeler (Terrasolid, Ltd.).

1

2010-03-05T00:00:00

During acquisition, two base stations were used to support the precise positioning
and orientation of the LiDAR sensor head. At times an additional base station set
at the Oxford Airport was used as a back-up. The base stations were positioned so
that the aircraft would be no further than 20-miles from a single base station at
any time during the flight and were placed on the control points established by Maptech
during the ground control phase of the project. The LiDAR acquisition commenced on
December 17, 2009 and was completed on March 5, 2010. Initial processing of the LiDAR
data determined that reflights were necessary; in part because of sensor or base station
malfunctions. The reflights occurred between June 27, 2010 and July 9, 2010. To achieve
better penetration of the vegetation during the reflights, two passes were conducted
over the reflight area; one in each direction. Detailed flight information and flight
logs can be found in the separate Flight Report submitted with the project.

1

2013-12-20T00:00:00

The NOAA Coastal Services Center (CSC) received topographic files in text format from
the Mississippi Department of Environmental Quality (MDEQ). The files contained lidar
easting, northing and elevation. The data were received in Mississippi State Plane
West 2302, NAD83 coordinates and were vertically referenced to NAVD88 using the Geoid03
model. The vertical and horizontal units of the data were feet. CSC performed the
following processing for data storage and Digital Coast provisioning purposes: 1.
The ASCII files were converted from txt format to las format using LASTools' txt2las
2. The LAS tiles were retiled to remove the buffer, then duplicate points were removed
3. The LAS tiles were then run through LASGround in order to extract surface classifications.
4. The las files were converted from orthometric (NAVD88) heights to ellipsoidal heights
using Geoid03. 5. The las files' vertical units were converted from feet to meters,
removing bad elevations. 6. The las files were converted from a Projected Coordinate
System (MS SP West) to a Geographic Coordinate system (NAD83) 7. The las files' horizontal
units were converted from feet to decimal degrees. 8. The data were converted to LAZ
format.

1

2013-12-31T00:00:00

The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp
transfer from the NOAA Coastal Services Center. The data are currently
being served via NOAA CSC Digital Coast at http://www.csc.noaa.gov/digitalcoast/.
The data can be used to re-populate the system. The data are archived in LAS or LAZ
format.
The LAS format is an industry standard for LiDAR data developed by the American Society
of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless compressed version
of
LAS developed by Martin Isenburg (http://www.laszip.org/). The data are exclusively
in geographic coordinates (either NAD83 or ITRF94). The data are referenced vertically
to
the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most
up to date geoid model when transforming to orthometric heights.